Project Summary: The long term goal of this application is to create a pure population of cardiac pacemaker cells from an easily accessible autologous cell type, the human hair follicle keratinocyte (HFKT-pacemakers), to characterize their pacemaker mechanism, their ability to integrate into the cardiac syncytium and their potential to function as an in vivo biological pacemaker. If successful in the long term, the health benefit of such an approach will be to substitute for the more than 350,000 electronic pacemakers implanted or reimplanted in patients in the United States each year. The project has four specific aims: (1) to expand the population of induced pluripotent stem cells created from the HFKTs, enhance their differentiation to a cardiac lineage and select for pacemaker myocytes; (2) to characterize the membrane currents in the HFKT- pacemakers as well as their pacemaker function and gene expression profile, and to compare the HFKT- pacemaker to native cardiac primary and secondary pacemakers in vitro; (3) to determine (a) the ability of HFKT pacemakers to couple to adult heart cells from specific locations (atrium or ventricle) in vitro and whether the pacing rate generated is target dependent (b) which connexins HFKT-pacemakers express and the ability of the HFKT-pacemakers to couple to cells expressing fibroblast connexins (a potentially arrhythmogenic situation); (4) to determine in vivo biological pacemaker function generated by placement of HFKT-pacemakers in the canine atrium or ventricle. Our approach will employ 1) novel methods to enhance selection of pacemaker cells, 2) patch clamping to characterize action potential morphology and membrane currents in the isolated pacemaker cells generated, 3) gene chips to determine the pacemaker cells' expression profile, 4) dual whole cell patch clamp, and biochemical and molecular techniques to determine connexin expression and functional cell to cell coupling 5) Injection of the HFKT- pacemakers into the canine atrium or ventricle to determine in vivo pacemaker function. The experiments will be carried out by a team of long term collaborators at Stony Brook University and at the Technion in Israel. The team has extensive expertise in stem cell biology, induced pluripotent stem cells, cardiac pacemaking, patch clamp,, and in vivo studies of biological pacemaker function. Successful execution of the research plan will enhance selection techniques for cardiac cell lineages from IPSCs, characterize the basis of pacemaker activity in the HFKT- pacemakers and determine their effectiveness as an in vivo biological pacemaker. If the HFKT-pacemaker functions well in the canine heart, a future goal would be to advance this novel autologous, cellular approach towards clinical deployment.